Constant velocity universal joints are well known in the art and are employed where transmission of a constant velocity rotary motion is desired or required. The tripod joint is characterized by a bell-shaped outer race (housing) disposed around an inner spider joint which travels in channels formed in the outer race. The spider-shaped cross section of the inner joint is descriptive of the three equispaced arms extending therefrom which travel in the tracks of the outer race. Part spherical rollers are featured on each arm.
One common type of constant velocity universal joint is the plunging tripod type, characterized by the performance of end motion in the joint. Plunging tripod joints are currently the most widely used inboard (transmission side) joint in front wheel drive vehicles, and particularly on the propeller shafts found in rear-wheel drive, all-wheel drive and four-wheel drive vehicles. Another common feature of tripod universal joints is their plunging or end motion character. Plunging tripod joints allow axial movement during operation without the use of splines which sometimes provoke significant reaction forces thereby resulting in a source of vibration and noise.
Tripod constant velocity joints are generally grease lubricated for life and sealed by an elastomeric sealing boot when used on some drive shafts. Most constant velocity universal joints are sealed in order to retain grease inside the joint while keeping contaminants and foreign matter, such as dirt and water, out of the joint. In order to achieve this protection, the constant velocity joint is usually enclosed at the open end of the outer race by a sealing boot made of rubber, thermoplastic or urethane. The opposite end of the outer race is sometimes formed by an enclosed "dome" known in the art as the greasecap. Such sealing and protection of the constant velocity joint is necessary because, once the inner chamber of the outer joint is partially-filled and thus lubricated, it is generally lubricated for life.
It is often necessary to vent the constant velocity joint in order to minimize air pressure fluctuations due to expansion and contraction of the air within the joint during operation of the joint. This is especially true in the case of a tripod-type constant velocity joints. Typically, constant velocity joints are vented by placing a small hole generally in the center of the greasecap. This allows for the passage of air in and out of the joint as needed, in order to prevent pressure buildup which occurs during operation of the joint.
However, when the constant velocity joint is in a static state and not rotating, grease may settle in the vent hole, blocking it and hindering its function. This condition may create a pressure buildup and possibly result in joint failure due to a ruptured boot, among other things. During this static state, grease may also flow from the vent hole and out of the joint, thereby resulting in the loss of grease from the joint. This loss of lubricant could possibly lead to more frequent relubrication and maintenance, and eventually possible replacement, of the joint. This is especially true in constant velocity joints with large filling masses of grease where, in a static state, the joint has a relatively large amount of grease stored therein which could flow out of a vent hole. This condition may equally occur when the constant velocity joint is in operation, but only at relatively low speeds.
U.S. Pat. No. 4,319,467 issued to Hegler et al. discloses a seal vent subassembly press fitted into the collar bore of a universal joint. The subassembly includes a vent disc which is nested in a seal disc to form a venting arrangement to the exterior of the housing by way of various holes and chambers. However, this vent hole may still be subject to grease buildup during a static state or operative state.
Consequently, an improved constant velocity joint design is provided which allows for reliable venting of the joint when large quantities of grease are contained therein, which also allows the vent to remain protected from grease buildup when the joint is in a static state or rotating at low speeds, and which facilitates venting when the joint rotates at high speeds.